The well-known Remote Authentication Dial in User Service or RADIUS set forth in Request For Comment or RFC 2865 and subsequently extended, such as in RFCs 2869 and 3576, has certain inherent limitations that spurred the IETF on to develop a replacement for AAA (Authentication-Authorization-Accounting) applications. That replacement standard is the well-known Diameter protocol set forth in RFC 3588.
Both 3GPP and 3GPP2 are swiftly moving towards Diameter. The Diameter-based credit control application, jointly supported by the IETF, 3GPP and 3GPP2, provides a framework that delivers online rating and charging capabilities to any network element through the open Diameter interface. Real-time processing of a large volume of rating and charging requests for a huge number of subscribers imposes a high performance demand on data access capabilities. Diameter is expected to meet this demand.
Accordingly, most of the next generation charging architectures are using Diameter as the standard charging interface for both online and offline charging. The IS-835 standard is a notable exception. The IS-835 standard defines the two methods for accessing public networks (Internet) and private networks (intranets): Simple IP and Mobile IP. IS-835C added prepaid charging support and defines the interface between PDSN (packet data serving node), HA (home agent), AAA, and prepaid server. It extended the use of RADIUS Access-Request to authorize prepaid access in addition to general access and provided an Online Access-Request to convey a subsequent credit control request from the PDSN/HA to the AAA/prepaid server. As stated, IS-835 standard uses RADIUS. The primary reasons for this are that Diameter was not ready in time to enable a prepaid solution for 1xRTT and EV-DO packet data services, and RADIUS has been widely deployed in many networks. However, from a prepaid vendor's perspective, supporting both RADIUS and Diameter based online/prepaid charging creates desired functionality and interface overlapping.
One of the applications in Diameter is the mechanical translation of RADIUS messages into Diameter messages. IETF RFC 3588 reserved AVP (attribute value pair) encoding space to support existing RADIUS attributes. IETF RFC 4006 defines the Diameter Network Access Server Application and attempts to achieve backward compatibility to RADIUS through translation. However, prepaid service authentication and authorization falls out of the scope of RFC 4006. Therefore, the mechanical translation is not applicable to IS-835 RADIUS.